1,720,991 research outputs found
Confinement of existing RC and masonry columns with FRCM composites: Aci-RileM provisions
No full textThe use of fiber reinforced cementitious mortar (FRCM) composites for repair/retrofitting existing reinforced concrete (RC) and masonry structures has gained increasing interest. Among the different applications of FRCM composites is the use for confinement of columns. Recent efforts have been made within the scientific community to investigate the response of FRCM-confined columns, and on the basis of available results, ACI guidelines have been published to support their design. On the other hand, scientific and technical commissions are also working in Europe, in some cases in conjunction with the related ACI committees, to harmonize design approaches and extend design relationships to existing structures typical of European countries. In this work the most relevant design issues related to FRCM confinement of RC and masonry columns are discussed in light of available experimental and theoretical results. Design relationships for American and European guidelines are presented, and critical aspects are identified to provide suggestions for future research and technical work
Investigation of the bond behavior of the fiber reinforced composite-concrete interface using the finite difference method (FDM)
No full textFiber reinforced composite materials, including fiber reinforced polymer (FRP) and fiber reinforced cementitious matrix (FRCM), have been widely used to increase the load-carrying capacity and ductility of concrete structures. The bond-slip relationship of the composite-concrete interface is of pivotal significance to understand the behavior of the strengthened structure. This study presents a generic and versatile finite difference method (FDM) solution that can predict the full-range bond behavior of the composite-concrete interface adopting different (e.g., bilinear, trilinear, exponential, and their combinations) bond-slip relationships. The proposed FDM solution successfully captures the snap-back phenomenon using an arc-length method for iteration. Comparison between FDM and analytical results shows that (i) for some frequently adopted analytical solutions, the assumption of zero slip at the composite free end is not suitable for short bonded lengths and fails to capture the snap-back phenomenon and load descending stage for long bonded lengths; (ii) for bond-slip relationships with different shapes, the load responses are similar but the effective bond lengths can be different when the same fracture energy is enforced; and (iii) for composite-concrete joints with finite bonded length, the peak load may not be the same when adopting different bond-slip relationships with the same fracture energy
Analytical study of the bond behavior of fiber reinforced cementitious matrix (FRCM)-substrate joints based on a two-stage nonlinear cohesive material law
No full textExternally bonding fiber-reinforced cementitious matrix (FRCM) composite to the surface of concrete or masonry members is an effective technique to improve the performance of existing structures. In many cases, interfacial debonding between the FRCM fiber textile and embedding matrix governs the capacity of FRCM-strengthened structures. The interfacial debonding process can be studied analytically by assuming a cohesive material law (CML), which represents the relationship between interfacial shear stress and slip. In this study, a two-stage function with an exponential stage and a constant stage is proposed to describe the CML associated with the matrix-fiber interface. The latter stage is characterized by a constant shear stress to account for the friction/interlocking between the matrix and fiber observed in experimental tests. With the assumed CML, the full-range loading response was obtained. Additionally, the interfacial slip, fiber axial strain, and interfacial shear stress were analytically derived. The parameters of the two-stage CMLs for PBO, glass, and carbon FRCM were inversely determined by matching the analytical relationships of peak applied axial stresses associated with different bonded lengths with the experimental ones. Considering the inversely determined CMLs, the predicted load responses and strain profiles showed good agreement with the measurements of direct shear test specimens
Estimation of the Shear Strength of RC Members with Externally Bonded, Fully-Wrapped FRCM Composites
No full textExternally bonded (EB) fiber reinforced cementitious matrix (FRCM) composites have been proven to be an effective solution for shear strengthening existing reinforced concrete (RC) members. Different layouts, namely U- and full-wrapping, of the EB composite can be adopted depending on the geometry and type of RC member. In the case of RC beams, the fully-wrapped layout is not always possible due to the presence of the slab. However, this layout is particularly attractive in the case of RC columns, where the composite can be applied easily and may provide significant strength increase. Although FRCM composites are attracting interest, the availability of analytical design models is still quite limited. In particular, few studies regarding the evaluation of the shear strength of FRCM fully-wrapped RC members are available in the literature. In this paper, an analytical model for the estimation of the contribution of fully-wrapped FRCM composites to the shear strength of RC members is proposed. The model is based on the truss analogy commonly adopted by various codes and guidelines for the estimation of the shear strength of RC beams and for fiber reinforced polymer (FRP) strengthened RC beams. The analytical model estimates the contribution of the FRCM to the member shear strength accounting for the bond behavior of the specific composite employed, which is an important aspect since FRCM composites have reported different bond behavior than FRP composites externally bonded to concrete substrates. The accuracy of the model provisions is assessed by comparing analytical and experimental results of RC beams fully-wrapped with a carbon FRCM composite
Shear Strengthening of RC Beams with U-Wrapped FRCM Composites: State of the Art and Assessment of Available Analytical Models
No full textShear strengthening of existing reinforced concrete (RC) members with externally bonded (EB) fabric-reinforced cementitious matrix (FRCM) composites represents an attractive solution with respect to alternative strengthening techniques. The EB FRCM could be side-bonded, U-wrapped, or fully wrapped around the beam cross section. Compared with analogous research on EB fiber-reinforced polymers (FRPs), limited work was performed to study the contribution of the EB FRCM to the shear strength of RC beams and was mainly focused on the U-wrapped configuration. Although various analytical models to estimate the EB FRCM shear strength contribution were proposed, their accuracy and the role of different parameters on the results obtained were not thoroughly investigated. In this paper, a state of the art on side-bonded and U-wrapped FRCM shear-strengthened RC beams is provided and discussed to highlight the knowledge gaps and identify the main parameters that control the member shear strength. The accuracy of the available analytical models for the U-wrapped configuration is assessed with respect to a database of experimental FRCM shear-strengthened RC beams collated from the literature. The results obtained point out the key features that the analytical model should have to provide accurate and reliable predictions
Flexural behavior RC beams strengthened and repaired with SRP composite
No full textThis paper presents the results of an experimental investigation conducted to study the flexural response of reinforced concrete (RC) beams strengthened and repaired using externally bonded steel reinforced polymer (SRP) composite. SRP composite strips were bonded to the tension face of four RC beams, which were tested in four-point bending. Parameters varied were the presence/absence of U-wrap anchorages and loading rate. The difference in the loading rates employed did not appear to have a significant effect on the yield load, maximum load, or failure mode. The strengthening system without anchorage increased the yield load by 16% relative to the control beam, whereas the strengthening system with U-wrap anchorages increased the yield load by 26–34% relative to the control beam. Values of the maximum strain in the composite at the maximum load of the strengthened beams with U-wrap anchorages ranged from 0.9% to 1.2% and were more than twice as large as that of the strengthened beam without anchorage. The peak fiber stress obtained from single-lap direct-shear tests of SRP-concrete joints was similar to the maximum fiber tensile stress obtained by sectional analysis for the strengthened beam without anchorage
Shear Strength Model for Reinforced Concrete Beams with U-Wrapped FRCM Composites Based on the Critical Shear Crack Width Evolution
No full textThis paper presents a new procedure to determine the different shear strength contributions of RC beams strengthened with U-wrapped externally bonded (EB) fiber-reinforced cementitious matrix (FRCM) composites. A main shear crack, named the critical shear crack (CSC), is assumed based on the compression chord capacity model (CCCM). Since the CCCM is originally an ultimate limit state model, a simplified hyperbolic function with a final value based on the CCCM is proposed to relate the concrete contribution to the CSC width, similarly to other models in the literature. Considering the truss analogy of the CCCM, i.e., adopting its angle of inclination of the compression struts, the procedure accounts for the presence of internal steel stirrups and U-wrapped EB FRCM that is modeled considering its bond behavior and tensile strength. The procedure allows for predicting the total shear strength and the different contributions, as shown by comparison between the analytical and experimental results of a 15-beam data set sourced from the existing literature. Notably, the relationship between the shear strength contributions and CSC width allows for some design advantages, particularly in terms of durability
Full-Range Behavior of Fiber Reinforced Cementitious Matrix (FRCM)-Concrete Joints using a Trilinear Bond-Slip Relationship
No full textInterfacial debonding of fiber reinforced cementitious matrix (FRCM)-concrete joints can be considered as a mainly mode-II fracture process, a problem that can be solved by accounting for one-dimensional interfacial shear stress-slip relationships. This paper presents an analytical approach to predict the load response of FRCM-concrete joints by adopting a trilinear bond-slip relationship consisting of a linear-elastic branch, a softening branch, and a friction branch. The applied load-global slip response of FRCM-concrete joints with (relatively) long bonded length includes five stages: elastic, elastic-softening, elastic-softening-debonding, softening-debonding, and debonding stages. Closed-form solutions of the interfacial slip, shear stress, and axial stress (or strain) distribution along the bonded length are provided. The response of FRCM-concrete joints with (relatively) short bonded length is examined. The effective bond length and a critical length for the existence of the snap-back phenomenon are derived. Experimental results reported in the literature are used to calibrate the parameters needed for the analytical approach. The analytical results are then compared with experimental results and with numerical results determined using a finite difference method (FDM). Finally, the capability of determining the parameters in the trilinear bond-slip relationship using a neural network (NN) with the experimental load response as the input is investigated
A Comparative Study of Bond Test Methods for Externally Bonded FRCM and SRG Composites
No full textThe bond behavior of externally-bonded fiber reinforced composites has been studied experimentally using different types of test methods. In this study the bond behavior of composite strips externally bonded to fired-clay brick masonry was tested using single-lap direct shear tests and hinged beam tests. The results obtained from the two test types were compared to investigate the effect of the test set-up on the load-carrying capacity of the matrix-fiber interface. Two different composite systems were considered: a fiber-reinforced cementitious matrix (FRCM) composite with a balanced bidirectional mesh of basalt fibers embedded in a hydraulic lime-based mortar, and a steel reinforced grout (SRG) with a sheet of ultra-high-strength unidirectional steel fiber cords embedded in the same mortar. The results are discussed and compared in terms of failure modes and applied load versus slip of the fibers response. An estimate of the matrix-fiber interfacial fracture energy of SRG-masonry joints is proposed using a global energy balance approach that does not require measurement of the strain in the fibers
Open issues on the investigation of PBO FRCM-Concrete debonding
No full textThis paper addresses some open issues of the bond behavior of fiber-reinforced cementitious matrix (FRCM)
composites applied to a concrete substrate. The study is focused on the effect of the number of fiber layers on the
peak load, the effect of the loading rate on the load response, the relationship between peak load and bonded
length (considering also bonded lengths substantially longer than the effective bond length), and the information
that can be gained by measuring the slip at the free end of the bonded composite. The FRCM composite
investigated is comprised of polyparaphenylene benzobisoxazole (PBO) fibers and a polymer-modified cementitious
mortar. The experimental results are compared with results from the literature. The results indicate that
the peak load must be carefully interpreted considering the effect of friction (interlocking), which is observed to
occur between fibers and matrix and the fibers themselves. In addition, the effect of the loading rate requires
additional investigation. Finally, the peak load of specimens with two layers of PBO fiber mesh is approximately
double the peak load of tests with one layer of fiber mesh if the bonded length is longer than the effective bond
length determined from tests with one layer of fiber mesh
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